1. Technical Field
The present disclosure relates to wireless power transmission systems and, in particular, to high efficiency wireless power systems.
2. Discussion of Related Art
Most wireless power systems use voltage-fed power stages that are, for example, consistent with the WPC qi standard or other wireless standards. These systems utilize either a half or full-bridge switching technologies. Typically, these implementations, as shown in system 100 illustrated in FIG. 1A, include an AC/DC power supply 102 that is connected to the AC main lines. Customary universal input voltage ranges vary from about 90 VAC to about 265 VAC at 50 or 60 Hz. Typically AC/DC power supply 102 includes a transformer and rectifier to produce a DC voltage, for example 5V, that is then used by the wireless power transmitter 104 to transmit power to the wireless power receiver 106. Safety regulations typically require that the output of the AC/DC power supply 102 be galvanically isolated from the AC mains for safety. This requires a safety rated transformer to be used in such power supplies, which decreases the efficiencies of these systems. FIG. 1B illustrates a system 100 as shown in FIG. 1A.
Typically, efficiencies for wireless transmitters are calculated from the wireless transmitters themselves. The wireless transmitter efficiency is typically calculated as
      Eff    TxRx    =      Pout    Pin  where Pout is the output power provided by the wireless power receiver 106 and Pin is the power received by the wireless power transmitter 104. This definition of power efficiency, however, is clearly inadequate and incomplete as it completely ignores the efficiency of AC/DC power supply 102 or any cabling, such as a USB cable, or other connector losses in system 100. In order to provide accurate efficiency standards, the overall efficiency from AC input to RX output has to be considered and that efficiency should be high. Consequently, the efficiency of the AC/DC power supply 102, which can be given by
      Eff    ad    =      Pin    PAC  where PAC is the input AC power, needs to be considered.
Typical efficiencies in AC/DC power supply 102 is between about 72-78%. This is often due to low adapter DC voltage output and more than 1 A current for 5 W delivery of power. Cable and connector losses can add up to 3% or more. The typical efficiency of the wireless power transceiver system formed by power transmitter 104 and power receiver 106 is about 72-75% in a conventional 5 W system wireless power transmission system. Consequently, the overall efficiency of a conventional system 100 is given by the multiple of the two (Effreal=Effad·EffTxRx), or about 54%.
Therefore, there is a need for better efficiency systems for transmitting power wirelessly.